(a) Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device of a stacked capacitor type memory cell having on a substrate a cylindrical member having a bottom and no top made of polysilicon, and more in particular to the method for manufacturing the semiconductor device having the stacked capacitor type memory cell equipped with a capacitor having a. large electrostatic capacity per occupied unit area.
(b) Description of the Related Art
Recently, in a semiconductor memory device such as DRAM (Dynamic Random Access Memory), a demand of decreasing a required area of each memory cell for attaining high integration is highly desired. In order to respond to this demand, it is important to form a capacitor having a large electrostatic capacity per occupied unit area in each of the memory cells.
The increase of the electrostatic capacity, of either of an upper electrode or a lower electrode of each of the capacitors, for example of the lower electrode, is attempted by employing a cylindrical electrode as the lower electrode. Moreover, the surface area of the electrode is increased by forming a layer of hemispherical silicon nuclei (HSG-Si: Hemi-Spherical Grained Si) on the cylindrical electrode surface to make the electrode surface uneven so as to further increase the electrostatic capacity.
First, a method for forming a conventional cylindrical lower electrode having the hemispherical silicon grains applied for making a stacked capacitor type memory cell will be described with reference to FIGS. 1 to 6. FIGS. 1 to 6 are sectional views suquentially showing the respective layered structures including a substrate of each of the steps for conducting the above method.
(1) In a conventional method, an element separation film 14 is formed on a silicon substrate 12, and a gate oxide film is formed in a region after the element separation as shown in FIG. 1. Then, the formation of gate electrodes 16A, 16B followed by that of source/drain diffusion regions 18 makes two adjacent n-MOSFETs.
Then, an interlayer insulation film 20 made of -a BPSG film and a first silicon oxide film 22 are successively formed on the whole substrate 12 surface.
Through holes for exposing the source regions 18 are perforated through the first silicon oxide film 22 and the interlayer insulation film 20, and the through holes are filled with phosphorus (P) doped amorphous silicon film (hereinafter referred to as xe2x80x9cP-doped Si filmxe2x80x9d) to make capacitance contact plugs 24 which are electrically connected with the source regions 18.
A silicon nitride film 26, a spacer layer 28 made of a BPSG film and a second silicon oxide film 30 are successively layered on the whole substrate surface. The patterning by means of photolithography is conducted to etch the second silicon oxide film 30, the spacer layer 28 and the silicon nitride film 26 to form openings (concaves) 32 for making lower electrodes. The layered structure shown in FIG. 1 is obtained.
(2) Then, a P-doped Si film between 1000 and 1500 xc3x85 is grown along the whole open walls of the openings 32 under the below conditions for growing an intermediate. layer 34 for forming the cylindrical lower electrode (hereinafter referred to as xe2x80x9ccylindrical member 34xe2x80x9d) as shown in FIG. 2. In FIG. 2, a numeral 36 designates an outer part of the P-doped Si film, or a phosphorous doped amorphous silicon originally grown layer (hereinafter referred to as xe2x80x9coriginally grown layerxe2x80x9d) in contact with the opening wall of the openings 32.
Conditions for Growing P-Doped Si Film
Reaction Gas: SiH4+PH3 
Temperature for Growing: 525 to 535xc2x0 C.
Pressure: 1.5 to 2.0 torr.
(3) Silica glass is then spin-coated on the whole substrate surface to form a silica film (SOG) which is etched back to obtain a layered structure having a silica layer 38 on the cylindrical member 34 as shown in FIG. 3. The silica layer 38 is employed for protecting the bottom part 35 of the cylindrical member 34 from being etched when the P-doped Si film is etched. A resist film or the like can be used in place of the silica film 38 as long as it functions as a protection film.
(4) The silica film 38 is then etched employing the second silicon. oxide film 30 as an etching stopper as shown in FIG. 4.
(5) The second silicon oxide film 30 and the spacer layer 28 are then etched employing the silicon nitride film 26 as an etching stopper to expose the outer and inner wall surfaces of the cylindrical member 34 made of the phosphorous doped amorphous silicon (lower electrode intermediate) as shown in FIG. 5.
(6) The silicon nitride film 26 employed as the etching stopper is then removed by the etching without etching the cylindrical member 34 to expose the first silicon oxide film 22 as shown in FIG. 6.
(7) After the above procedures are completed, the cylindrical member 34 is subjected to a treatment for making hemispherical silicon grains employing a reaction furnace preferably in a batchwise operation as follows. The above treatment of the cylindrical member 34 may be performed successively in a sheetwise operation.
(i) A wafer having the above layered structure is sent to the reaction furnace, and a temperature is elevated under high vacuum to 560xc2x0 C. and maintained for 30 minutes. This step is called a temperature stabilization step.
(ii) An SiH4 gas is introduced into the reaction furnace at a rate of 75 sccm while maintaining the temperature of 560xc2x0 C. and the wafer is irradiated with the above gas for 20 minutes. Si crystal nuclei are thereby formed on the P-doped Si film 34. This step is called an SiH4 irradiation step.
(iii) The wafer is then subjected to an annealing treatment under high vacuum maintaining the temperature of 560xc2x0 C. The Si crystal nuclei are thereby grown to become the hemispherical grains by means of integrating the silicon atoms in the P-doped Si film on the Si crystal nuclei formed on the P-doped Si film. This step is called an annealing step. During the treatment of making the hemispherical grains, the P-doped Si film is converted into a phosphorous doped polysilicon film by means of the annealing treatment.
After the above procedures, the surface of the cylindrical member 34 has been formed by the hemispherical grains.
In the above treatment, however, among the hemispherical silicon grains formed on the surface of the cylindrical member 34, those on the outer wall surface have non-hemispherical grain surfaces 42 and uneven shapes though those on the inner wall surface have hemispherical grain surfaces 40 of a uniform and preferable grain radius as shown in FIG. 7. Moreover, the grain size of the former becomes excessively large so that the respective grains are in contact with one another not to increase the surface area of the cylindrical member to an expected value.
With the miniaturization of memory cells, a cell pitch between the memory cells becomes extremely small, and an interval between two adjacent cylindrical lower electrodes becomes short accordingly. For example, in the direction of a shorter side of the lower electrode, a width of the cylindrical member is 0.25 to 0.40 micronmeter while an interval between the electrodes is 0.15 to 0.18 micronmeter. On the other hand, in direction of a longer side of the lower electrode, a width of the cylindrical member is 0.70 to 0.78 micronmeter while an interval between the electrodes is 0.20 to 0.23 micronmeter. These intervals are extremely short. When, therefore, the grain size 42 becomes excessively large, the outer walls of the adjacent cylindrical members are likely to be in contact with each other via the grains to produce a short-circuit between the adjacent electrodes.
These defects may reduce the effectiveness of producing the hemispherical grains on the surface of the cylindrical member, and the realization of the memory cell having a large electrostatic capacity is difficult, and the memory cell having a high electrical reliability and no fear of short-circuit can be hardly provided, or the yield of the memory cells is lowered.
It is, therefore, an object of the present invention to provide a method for manufacturing a semiconductor device having a highly reliable stacked capacitor type memory cell equipped with a capacitor having a large electrostatic capacity per occupied unit area and no fear of generating short-circuit or the like.
The present invention provides a method for manufacturing a semiconductor device having a substrate and a cylindrical member formed thereon comprising,
a step of forming a spacer layer made of etchable material on the substrate,
a step of making a concave in the spacer layer,
a step of making an amorphous silicon film along the concave to form an amorphous silicon cylindrical member having the amorphous silicon film as a cylindrical wall thereof,
an exposure step of etching the spacer layer to expose the inner and outer wall surfaces of the amorphous silicon cylindrical member,
a removal step of removing the outer wall surface layer of the amorphous silicon cylindrical member by mean of etching,
a step of treating the outer and inner wall surfaces of the amorphous silicon cylindrical member to form hemispherical silicon grains thereon to convert the amorphous silicon cylindrical member into a polysilicon cylindrical member of which outer and inner wall surfaces have the hemispherical silicon grains.
The present invention also provides a method for manufacturing a semiconductor device having- a substrate and a cylindrical member formed thereon comprising,
a step of forming a spacer layer made of etchable material on said substrate,
a step of making a concave in said spacer layer,
a step of making an amorphous silicon film along said concave to form an amorphous silicon cylindrical member having said amorphous silicon film as a cylindrical wall thereof,
an exposure step of etching said spacer layer to expose the inner and outer wall surfaces of said amorphous silicon cylindrical member,
a step of treating the outer and inner wall surfaces of the amorphous silicon cylindrical member to form hemispherical silicon grains thereon to convert the said amorphous silicon cylindrical member into a polysilicon cylindrical member of which outer and inner wall surfaces have the hemispherical silicon grains, and
said treatment step further comprising,
a first step of elevating a temperature of the amorphous silicon cylindrical member to a prescribed temperature while flowing a hydrogen gas and/or a phosphin gas into a reaction furnace accommodating the substrate having said amorphous silicon cylindrical member and maintaining the cylindrical member at the prescribed temperature for a first prescribed period of time,
a second step of introducing an SiH4 gas into the reaction furnace and irradiating said cylindrical member with said SiH4 gas for a second prescribed period of time while maintaining said cylindrical member at the prescribed temperature, and
a third step of maintaining said cylindrical member at the prescribed temperature under vacuum and of thermally treating
said cylindrical member to convert said member into said polysilicon cylindrical member.
The present invention further provides a method for manufacturing a semiconductor device having a substrate and a cylindrical member formed thereon comprising,
a step of forming a spacer layer made of etchable material on said substrate,
a step of making a concave through said spacer layer,
a cylindrical member formation step of making an amorphous silicon film along said concave to form an amorphous silicon cylindrical member having said amorphous silicon film as a cylindrical wall thereof,
an exposure step of etching said spacer layer to expose the inner and outer wall surfaces of said amorphous silicon cylindrical member,
a step of treating the outer and inner wall surfaces of the amorphous silicon cylindrical member to form hemispherical silicon grains thereon to convert the said amorphous silicon cylindrical member into a polysilicon cylindrical member of which outer and inner wall surfaces have the hemispherical silicon grains, and
said cylindrical member formation step further comprising,
a first step of forming a first amorphous silicon film having a thickness between 50 and 80 xc3x85 along the wall of said concave under a temperature between 490 and 510xc2x0 C. and a pressure between 0.3 and 1.0 torr. while introducing an SiH4 gas and a phosphine gas into a reaction furnace accommodating the substrate having the concave in the spacer layer, and
a second step of forming a second amorphous silicon film on the first amorphous silicon film while maintaining conditions of a temperature between 525 and 535xc2x0 C. and of a pressure between 1.5 and 2.0 torr. after elevating the temperature at a rate of 2 to 5xc2x0 C./min. and the pressure at a rate of 0.1 to 0.3 torr./min.
In accordance with each of the methods of the present invention, the amorphous silicon cylindrical member having on the inner and outer wall surfaces the hemispherical grains having a uniform grain size can be obtained by (1) removing in advance the originally grown layer before forming the hemispherical grains, by (2) growing the amorphous silicon film under the conditions of suppressing the growth of the amorphous silicon film, or by (3) controlling the growth of the hemispherical grains on the originally grown layer in the temperature stabilization step.
The semiconductor device equipped with a capacitor having a remarkably increased surface area per unit electrode surface, a large electrostatic capacity and no connection deficiency such as short-circuit can be obtained by applying the method of the present invention to the manufacture of the above semiconductor device.